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Politics : Evolution -- Ignore unavailable to you. Want to Upgrade?


To: TigerPaw who wrote (1180)8/13/2000 11:07:55 PM
From: TigerPaw  Read Replies (1) | Respond to of 69300
 
Eyes
Assume man had no eyes and we needed to form them. What do we need from random chance? DNA changes
would have to occur to effect nervous, skeletal, muscular, vascular and endocrine systems - all at
once, to form. 2 bony orbits in skull to house the eyes with holes (foramina) for nerves and
vessels. Globe - sclera, choroids, and retina with its rods and cones and specialized visual
chemicals, vitreous body, lens, suspensory ligament and ciliary muscle, iris (with its control
nerves) cornea, aqueous humor, canal of schlemm, and internal circulation of blood. Muscles
with nerves to control eye movements. Optic nerves with crossover pathways. Visual cortex in
the brain with the ability to fuse the images and interpret the millions of nerve signals each second
and connect with the rest of consciousness in the brain. Vestibular mechanism and also the life
saving spinal cord reflexes. All features must be perfectly integrated and balanced with all other
systems. Plus we need eyebrows, eyelids, eyelashes, conjunctive, tear glands, tear ducts,
pigment for the iris and genes to control the color (Drosophila has 15 genes to control eye
color). If everything in not just right,
it would be worse than no eyes at all. (Try wearing your neighbor's glasses!)


Ugg, there are plenty of web sites to show that all vision forms from simple photodetectors - such as the back of your arm which will feel "hotter" on the side facing the sun - to the greatest of eyes (which are not human) are all still available as examples in living animals. Each improvement is a slight change, but conveys a distinct advantage in the appropriate circumstance. Eyes have evolved multiple times.
TP